柴油机喷嘴内线空化对喷雾影响的试验
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摘要
设计3种不同尺寸的锥度孔透明喷嘴,在尽可能抑制壁面空化的情况下研究了喷油压力、喷嘴孔尺寸及针阀升程对喷嘴内线空化的出现规律、强度及瞬态特性的影响,进而对喷雾的影响.结果表明:在喷嘴低针阀升程时会存在起源于针阀锥面处的线空化,可轻易延伸至喷孔出口,形态粗壮,引致非常大的喷雾锥角,而随针阀的抬起,这类线空化消失,代之以孔与孔之间的线空化,空化形态较细,对喷雾锥角影响相对很小,这为柴油机启喷阶段和喷油末期喷雾锥角的骤增与波动提供了一种合理解释;喷雾锥角的波动与线空化发展程度及其延伸至喷孔出口处的空化厚度间存在强烈的依存关系;线空化对喷雾的影响存在迟滞现象,这与空化泡喷出喷孔后破裂及流体运动惯性有关.
Three different dimensions of the transparent nozzles with tapered orifices were designed in order to eliminate the occurrence of the normal cavitation. The influence of injection pressure,nozzle size and needle lift on the occurrence,intensity,transient changes of the string cavitation,and thus on the spray characteristics. It is found that thick and strong kind of string cavitation always occurs on the tapered needle valve surface when the needle lift is small,leading to a bigger spray angel. As the needle lifts up,the thick and strong kind of string cavitation disappears and is replaced by another slimmer kind of hole-to-hole string cavitation,which has a little influence on the spray angel. This provides a reasonable explanation for sudden increase and fluctuation of the spray angle during the beginning and the end of injection behavior. The research results also indicate that the spray angle has a strong relationship with the string cavitation development and the bubble thickness at the valve exit. A hysteresis phenomenon exists during the influence of the string cavitation on the spray atomization,which is related to the time of cavitation bubble fracturing outside and the inertia of fluid motion inside.
Three different dimensions of the transparent nozzles with tapered orifices were designed in order to eliminate the occurrence of the normal cavitation. The influence of injection pressure,nozzle size and needle lift on the occurrence,intensity,transient changes of the string cavitation,and thus on the spray characteristics. It is found that thick and strong kind of string cavitation always occurs on the tapered needle valve surface when the needle lift is small,leading to a bigger spray angel. As the needle lifts up,the thick and strong kind of string cavitation disappears and is replaced by another slimmer kind of hole-to-hole string cavitation,which has a little influence on the spray angel. This provides a reasonable explanation for sudden increase and fluctuation of the spray angle during the beginning and the end of injection behavior. The research results also indicate that the spray angle has a strong relationship with the string cavitation development and the bubble thickness at the valve exit. A hysteresis phenomenon exists during the influence of the string cavitation on the spray atomization,which is related to the time of cavitation bubble fracturing outside and the inertia of fluid motion inside.
引文
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[3]黄豪中,安彦召,苏万华,等.喷射压力和喷孔直径对柴油机混合燃料喷雾特性的影响[J].内燃机学报,2013,31(3):200-207.
[4]邵壮,何志霞,钟汶君,等.柴油与生物柴油不同长径比喷嘴内空穴流动的试验[J].内燃机学报,2014,32(4):322-327.
[5]陶希成,何志霞,钟汶君,等.喷孔锥度对内流及喷雾影响的试验研究[J].工程热物理学报,2016,37(7):1572-1576.
[6]Gavaises M,Andriotis A,Papoulias D,et al.Characterization of string cavitation in large-scale diesel nozzles with tapered holes[J].Physics of Fluids,2009,21(5):114.
[7]Mitroglou N,Gavaises M,Nouri J M,et al.Cavitation inside enlarged and real-size fully transparent injector nozzles and its effect on near nozzle spray formation[J].Proceedings of the Dipsi Workshop Droplet Impact Phenomena&Spray Investigations,2011,10(4):525-589.
[8]Watanabe H,Nishikori M,Hayashi T,et al.Visualization analysis of relationship between vortex flow and cavitation behavior in diesel nozzle[J].International Journal of Engine Research,2014,16(1):5-12.
[9]王谦,孙伟,何志霞,等.基于超高速摄影分析柴油机近场喷雾锥角变化特性[J].农业工程学报,2016,32(15):47-53.
[10]张正洋,何志霞,郭根苗,等.柴油机原型喷嘴内瞬态流动的特性试验[J].内燃机学报,2017,35(2):136-141.
[2]He Z,Zhang Z,Guo G,et al.Visual experiment of transient cavitating flow characteristics in the real-size diesel injector nozzle[J].International Communications in Heat&Mass Transfer,2016,78:13-20.
[3]黄豪中,安彦召,苏万华,等.喷射压力和喷孔直径对柴油机混合燃料喷雾特性的影响[J].内燃机学报,2013,31(3):200-207.
[4]邵壮,何志霞,钟汶君,等.柴油与生物柴油不同长径比喷嘴内空穴流动的试验[J].内燃机学报,2014,32(4):322-327.
[5]陶希成,何志霞,钟汶君,等.喷孔锥度对内流及喷雾影响的试验研究[J].工程热物理学报,2016,37(7):1572-1576.
[6]Gavaises M,Andriotis A,Papoulias D,et al.Characterization of string cavitation in large-scale diesel nozzles with tapered holes[J].Physics of Fluids,2009,21(5):114.
[7]Mitroglou N,Gavaises M,Nouri J M,et al.Cavitation inside enlarged and real-size fully transparent injector nozzles and its effect on near nozzle spray formation[J].Proceedings of the Dipsi Workshop Droplet Impact Phenomena&Spray Investigations,2011,10(4):525-589.
[8]Watanabe H,Nishikori M,Hayashi T,et al.Visualization analysis of relationship between vortex flow and cavitation behavior in diesel nozzle[J].International Journal of Engine Research,2014,16(1):5-12.
[9]王谦,孙伟,何志霞,等.基于超高速摄影分析柴油机近场喷雾锥角变化特性[J].农业工程学报,2016,32(15):47-53.
[10]张正洋,何志霞,郭根苗,等.柴油机原型喷嘴内瞬态流动的特性试验[J].内燃机学报,2017,35(2):136-141.